Plants respond to light intensity, direction, duration, and spectral quality by modulating their developmental processes in an array of interactions that are referred to as photomorphogenesis. Photomorphogenic mutants have been proven to be an excellent tool in research of the complex interactions between light and plant development and some of them have also been used in several agricultural crop breeding programs. Photomorphogenic mutants have been reported in a number of species, including Arabidopsis, Sorghum, Brassica, tobacco, tomato and pea. In general, these mutants may be classified either as defective in photoreceptors, or altered in some aspect of light signal transduction chain (Chory, 1993).
Several photomorphogenic mutants have been described in tomato (lycopersicon esculentum). Among these, mutants carrying the monogenic recessive high pigment (hp-1, hp-1w, hp-2, and hp-2j) and dark green (dg) mutations are characterized by their exaggerated light responsiveness.
These mutants display higher anthocyanin levels, shorter hypocotyls, and greater fruit pigmentation in comparison to their semi-isogenic wild type plants (Mochizuki and Kamimura 1984; Wann et al. 1985). The increased fruit pigmentation seen in these mutants is due to significantly elevated levels of carotenoids, primarily lycopene, and flavonoids in the mature ripe red fruit. As a consequence of their effect on fruit color, hp and dg mutations were introgressed into several commercial processing and fresh-market tomato cultivars that are currently marketed as Lycopene Rich Tomatoes (LRT) (Wann, 1997).
The hp-1 mutant was originally discovered as a spontaneous mutant in 1917 at the Campbell Soup Company farms (Riverton, N.J.) (Reynard, 1956), The hp-1w mutant appeared among progeny of a plant raised from ethyl methanesulfonate (EMS)-treated seeds of the genotype GT (Peters et al. 1989), the hp-2 mutant was reported in the Italian San Marzano variety in 1975 (Soressi 1975), the hp-2j mutant was found among progeny of a T-DNA-transformed plant (cv Moneymaker) (van Tuinen et al. 1997), and the dg mutant appeared in trellised planting of the Manapal variety (Konsler 1973). Despite some initial confusion, it is now clear that there are two HP genes—HP-1 and HP-2—in the tomato genome, that map to chromosomes 2 and 1, respectively (van Tuinen et al. 1997; Yen et al. 1997). (Van Tuinen et al. 1997; Yen et al. 1997). At each of these loci, two of the above mentioned mutant alleles have been initially identified: hp-1 and hp-1w, hp-2 and hp-2j (Kerckhoff and Kendrick 1997; Van Tuinen et al. 1997).
WO 99/29866 discloses the cloning and sequencing of the HP-2 gene, said gene being found to encode the tomato homolog of the Arabidopsis nuclear protein DEETIOLATED1 (DET1).
This publication further discloses that a point mutation and deletion mutation, both of which are located in exon 11 at the 3′ end of the coding sequence of HP-2, give rise to the previously-identified hp-2j and hp-2 mutants respectively. In the case of the hp-2 mutant, a point mutation directs alternative splicing of intron 10 that leads to a nine base pair deletion in exon 11.
Co-owned WO 03/57917 discloses another point mutation in the tomato homolog of the Arabidopsis DET1 gene that is responsible for the dg mutation, and which therefore comprises a 3rd mutant allele at the HP-2 locus.
It is a purpose of the present invention to provide isolated nucleotide sequences containing the mutations responsible for the high pigment-1 (hp-1) and high pigment-1w (hp-1w) photomorphogenic mutants of tomato plants.
It is a further purpose of the present invention to provide DNA markers that may be used as a molecular diagnostic tool for the identification and selection of hp-1 and hp-1w mutants.
A yet further purpose of the present invention is to provide molecular diagnostic tools that may be used for genotypic selection in the production of lycopene-enhancing double mutants.
Other purposes and advantages of the present invention will become apparent as the description proceeds.